intracapsular ligament

Hip

In anatomy, the hip is the bony projection of the femur which is known as the greater trochanter, and the overlying muscle and fat. The hip joint, scientifically referred to as the acetabulofemoral joint, is the joint between the femur and acetabulum of the pelvis and its primary function is to support the weight of the body in both static (e.g. standing) and dynamic (e.g. walking or running) postures.

Description of the bones of the hips

The hip bones are divided into 5 areas, which are:

The sacrum: This is a bone at the base of the vertebral column that is created by the fusion of 5 vertebrae. It attaches to the ilium on the sides. It also provides a point of muscle attachment for back muscles.

The coccyx (also called the tail bone): This is a small vestigial bone that attaches to the base of the sacrum. It is created from the fusion of up to 5 small vertebrae.

The ilium: This is the largest area of the hip bones. It consists of 2 large broad plates, one on each side, which serve to support the internal organs, and to provide attachment for muscles of the back, sides, and buttocks. The hip joint of the femur is part of the ilium.

The ischium: The ischium consists of 2 broad curves of bone, one on each side, which lie below the ilium, and are attached to the pubis in the front and the ilium in the back. The ischium serves as a place of attachment for muscles. The ischium may press into the buttocks during long periods of sitting and may be a source of irritation.

The pubis: The pubis is the front-most area of the hip bones. It attaches to the ilium on the sides and the ischium on the bottom. It provides structural support, and serves as a place of attachment for the muscles of the inner thigh.

A synovial joint that can produce movement around more than one axis is called a multiaxial joint.

Anatomy of the hip joint

Articulation

The hip joint (latin articulatio coxae) is a synovial joint formed by the articulation of the rounded head of the femur and the cup-like acetabulum of the pelvis. It is classified as a ball and socket joint. It forms the primary connection between the bones of the lower limb and the axial skeleton of the trunk and pelvis. Both joint surfaces are covered with a strong but lubricated layer called articular hyaline cartilage. The cuplike acetabulum forms at the union of three pelvic bones and the joint may not be fully ossified (the process of forming bone) under the age of 25 years. The depth of the acetabulum is increased by a fibrocartilaginous rim called a labrum that grips the head of the femur and secures it in the joint. The acetabulum is oriented inferiorly, laterally and anteriorly. The magnitude of inferior orientation can be assessed using a line connecting the lateral rim of acetabulum and center of femoral head. This lines forms an angle with vertical known as center edge angle or angle of Wiberg. The magnitude of anterior orientation is referred as angle of acetabular anteversion.

The large head of the femur is completely covered in hyaline cartilage except for a small area called the fovea or pit. This is the site of attachment for an intracapsular ligament (called the ligamentum teres) that attaches directly from the head of the femur to the acetabulum. The head of the femur is attached to the shaft by a thin neck region that is often prone to fracture in the elderly, which is mainly due to the degenerative effects of osteoporosis.

Capsule

The strong but loose fibrous capsule of the hip joint permits the hip joint to have the second largest range of movement (second only to the shoulder) and yet support the weight of the body, arms and head. The capsule is attached proximally to the entire periphery of the acetabulum beyond the acetabular labrum. The capsule covers the femoral head and neck like a sleeve and attaches to the base of neck. The capsule has two sets of fibers: longitudinal and circular. The circular fibers form a collar around the femoral neck called the zona orbicularis. The longitudinal retinacular fibers travel along the neck and carry blood vessels. As the line of gravity falls posterior to the axis of the hip joint, the combined weight of the body seeks to extend the hip joint in normal standing and make the trunk fall backwards to the ground. To resist the stretching action on the anterior joint capsule in normal upright posture, the hip has two very strong anterior ligaments.

Ligaments

The hip joint is reinforced by three main ligaments.

At the front of the joint, the strong iliofemoral ligament attaches from the pelvis to femur. This Y-shaped ligament is also known as the ligament of Bigelow. This ligament seeks to resist excessive extension of the hip joint. It is often considered to be the strongest ligament in the human body.

The pubofemoral ligament attaches across the front of the joint from the pubis bone of the pelvis to the femur. This ligament is oriented more inferiorly than the iliofemoral ligament and reinforces the inferior part of the hip joint capsule. It also blends with the medial parts of the iliofemoral ligament.

The posterior of the hip joint capsule is reinforced by the ischiofemoral ligament that attaches from the ischial part of the acetabular rim to the femur.

There is also a small ligament called ligamentum teres or the ligament of the head of the femur. The ligament is a triangularly shaped band with its base on both sides of peripheral edge of acetabular notch. This structure is not that important as a ligament but can often be vitally important as a conduit of a small artery to the head of the femur. This arterial branch is not present in everyone but can become the only blood supply to the bone in the head of the femur when the neck of the femur is fractured or disrupted by injury in childhood.

Many of the hip muscles are responsible for more than one type of movement in the hip, as different areas of the muscle act on tendons in different ways.

Sexual dimorphism in humans

In humans, unlike other animals, the hip bones are substantially different in the two sexes. The hips of human females are wider than those of males. The femurs are also more widely spaced in females, so as to widen the opening in the hip bone and thus facilitate childbirth. Finally, the ilium and its muscle attachment are shaped so as to situate the buttocks away from the birth canal, where contraction of the buttocks could otherwise damage the baby.

Cultural significance of hips

The female hips have long been associated with both fertility and general expression of sexuality. Since broad hips facilitate child birth and also serve as an anatomical cue of sexual maturity, they have been seen as an attractive trait for women for thousands of years. Many of the classical poses women take when sculpted, painted or photographed, such as the Odalisque, serve to emphasize the prominence of their hips. Similarly, women's fashion through the ages has often drawn attention to the girth of the wearer's hips.